Air integration battery status (Suunto)

[Andreas Krueger]

Since 10 October 2025, the battery level of the air integration transmitters has been missing from the additional data.

Is this data no longer being processed intentionally, or is it a glitch?
HW: Suunto EON Steel
SW: Subsurface Mobile for iOS 6.0.5436 

Regards @ndreas

[Dirk Hohndel]

In the past I have noticed that Suunto transmitters cleverly stop transmitting their battery level once they reach... some value, and I don't recall what that was. But it was shockingly high, maybe 40%? So yeah, at the very time when I wanted that data most, it stopped showing up.

[Andreas Krueger]

Dear Dirk

Then I'll just change them. The last reported status was 19%.

However, the bottle pressure is still logged properly.

Thanks for the information.

Regards @ndreas

[Linus Torvalds]

On Thu, 30 Oct 2025 at 08:42, Andreas Krueger <webh...@gmail.com> wrote:
>
> Then I'll just change them. The last reported status was 19%.
> However, the bottle pressure is still logged properly.

Yeah, the issue is almost certainly that past a certain voltage level,
the battery life estimates just get so unreliable that Suunto went
"we'd rather not report any battery at all, than report a possibly
very incorrect battery level".

If I recall correctly, it's a 3V lithium battery in those things, and
if you google for "3V lithium battery voltage curve", you'll see that
the voltage - which is what the device uses to estimate battery life -
has a fairly linear slope between in the 20-80% region, but then in
the last 10-15% it really drops off a cliff.

As Dirk said, early Suunto tank pods used to actually stop reporting
much earlier. I think they updated the firmware - or possibly even
hardware - on those things.

And yes, it's confusing. We thought we had a bug in downloading the
first time we saw it too.

Linus

[Michael Keller]

Hi all.

On 31/10/25 05:00, Linus Torvalds wrote:
> On Thu, 30 Oct 2025 at 08:42, Andreas Krueger <webh...@gmail.com> wrote:
>> Then I'll just change them. The last reported status was 19%.
>> However, the bottle pressure is still logged properly.
> Yeah, the issue is almost certainly that past a certain voltage level,
> the battery life estimates just get so unreliable that Suunto went
> "we'd rather not report any battery at all, than report a possibly
> very incorrect battery level".
>
> If I recall correctly, it's a 3V lithium battery in those things, and
> if you google for "3V lithium battery voltage curve", you'll see that
> the voltage - which is what the device uses to estimate battery life -
> has a fairly linear slope between in the 20-80% region, but then in
> the last 10-15% it really drops off a cliff.

Interesting bit of engineering. Reminds me of the old Uwatec dive
computers with non-user-replacable batteries that would often go from
'90% battery left' to exhaustion within a single dive, which effectively
killed their resale value. Clearly, Suunto did it better by using
non-linear interpolation for the battery level.


Could Subsurface improve the user experience here if we showed something
like 'transmitter battery level < 20%, consider replacing' if a
transmitter is detected that does not send a battery level?


Ngā mihi

  Michael Keller

[Dirk Hohndel]

I believe we actually don't know what that threshold percentage is. So I'm not sure we could tell WHY we don't have transmitter data.

/D

[Michael Keller]

Hi Dirk.

On 31/10/2025 10:18, 'Dirk Hohndel' via Subsurface Divelog wrote:
> I believe we actually don't know what that threshold percentage is. So
> I'm not sure we could tell WHY we don't have transmitter data.

Do we need to know though - I think it would already be helpful to add
info telling the user that their transmitter battery is possibly about
to run out of power in cases where we detect that we get transmitter
pressure data, but no transmitter battery status data for Suunto
transmitters.

Compared to the current situation that is confusing to the user, this
will at least give them a chance to realise that they need to replace
the battery, or else risk having to abort a dive when their transmitter
goes flat.


Ngā mihi

  Michael Keller

[Edward Haynes]

Hi All,

My first Suunto, paired with a EON Steel, transmitter battery showed up on Subsurface right up to when it died, the last percentage reading was 1%. The 2 replacement batteries haven’t recorded their remaining percentage. The last one died after 250 dives over 3 years.

When I change the batteries in an AED unit I have, there is a ‘hidden’ reset button (to reset the battery monitoring software) inside the unit.

Does the Suunto transmitter have a similar reset button? I had a quick look on the last battery change, but was reluctant to play with the wiring.

Is there a Suunto wizard in the group who knows whether there is a battery reset button?

Kind regards

Edward

Edward Haynes
DO Fyne-divers
+44 (0) 7800 590112

BSAC
Dive with us

> On 31 Oct 2025, at 04:59, Michael Keller <mike...@042.ch> wrote:
>
> Hi Dirk.

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[Linus Torvalds]

On Thu, 30 Oct 2025 at 22:00, Michael Keller <mike...@042.ch> wrote:
>
> Do we need to know though - I think it would already be helpful to add
> info telling the user that their transmitter battery is possibly about
> to run out of power in cases where we detect that we get transmitter
> pressure data, but no transmitter battery status data for Suunto
> transmitters.

I think some warning when we do have pressure readings but no battery
reading might be reasonable.

So something like "you have a Suunto tank pod that doesn't generate
battery information - your battery may be weak" might be reasonable.

And I just refreshed my memory: apparently the Suunto tank pods (as
opposed to the older suunto wireless transmitters) actually use SAFT
batteries.

They are great batteries - and expensive - and not the usual Lithium
ones (still using it, but apparently LiSOCl2 chemistry).

Their voltage curve is actually very flat indeed, and then they
completely fall off a cliff when they are done. Even more so than
"regular" lithium batteries.

Going by the voltage curves I find with google that SAFT has in their
datasheets, the voltage curve is so flat that I would expect that
you'd have to do something else than track the voltage for remaining
battery life.

So I was probably wrong on the "use the voltage to estimate remaining
battery life". There might be something else going on. Maybe a lot of
guesstimating.

The end result is not that different, though: I suspect it's hard to
get reliable numbers, so at some random point the firmware in those
tank pods probably goes "I don't know, and I can't even guess" and
then the battery percentages stop being reported.

Linus

[Michael Keller]

Hi Linus.

On 1/11/25 03:48, Linus Torvalds wrote:
> On Thu, 30 Oct 2025 at 22:00, Michael Keller <mike...@042.ch> wrote:
>> Do we need to know though - I think it would already be helpful to add
>> info telling the user that their transmitter battery is possibly about
>> to run out of power in cases where we detect that we get transmitter
>> pressure data, but no transmitter battery status data for Suunto
>> transmitters.
> I think some warning when we do have pressure readings but no battery
> reading might be reasonable.
>
> So something like "you have a Suunto tank pod that doesn't generate
> battery information - your battery may be weak" might be reasonable.
>
> And I just refreshed my memory: apparently the Suunto tank pods (as
> opposed to the older suunto wireless transmitters) actually use SAFT
> batteries.
>
> They are great batteries - and expensive - and not the usual Lithium
> ones (still using it, but apparently LiSOCl2 chemistry).

They are great in terms of performance indeed.

But unfortunately their 'exotic' chemistry puts them into the 'other
batteries' category with most courier services, which means they
straight out refuse to ship them by air. As a consequence, availability
seems to be a problem in a lot of places. So for divers using Suunto
Tank PODs it is probably a good idea to carry a spare on international
trips.

> So I was probably wrong on the "use the voltage to estimate remaining
> battery life". There might be something else going on. Maybe a lot of
> guesstimating.

Based on the fact that there seems to be only one brand / model of
battery that is supported, with a known initial capacity, and that
battery replacement is hard and risky enough to allow the assumption
that nobody will be putting a half-used battery into a POD, I suspect
that they might just be counting the runtime hours, or number of
measurements made and sent, and extrapolate remaining battery life from
this.


Ngā mihi

  Michael Keller